I. Field of the Invention
The present invention relates to building construction, and more particularly to a structure and a method of construction for a roof system useful on both new and old buildings.
II. Description of the Prior Art
One major goal of designing roof systems is to provide the optimum combination of insulating, weatherproofing and fireproofing characteristics, achieved by the most lightweight construction possible. Such a task is often made difficult because of the characteristics of the particular materials employed. For example, materials that are fireproof may not be weatherproof or have any value as insulating materials. Thus, more than one material may be required to perform these various functions. A plurality of disparate materials will add weight to the entire roof system, sometimes necessitating strengthening of the load bearing walls and the addition of further structure to support the roof.
Present designs which focus primarily on the weatherproofing function typically consist of multiple layers of asphaltic felt, joined to each other and to the roof deck by bituminous material. Such designs are subject to the drawback that they provide minimal insulation or fireproofing. It is true that insulating properties can be provided in such a system by the addition of materials such as foam, plywood sheets or other insulation material. However, such added material must normally be protected from the elements (such as sunshine, moisture and changes in temperature) by a layer of asphaltic mastic and gravel.
These design elements are commonly referred to as the IRMA system, and are substantially disclosed in U.S. Pat. No. 3,411,256. This system first comprises a membrane disposed adjacent to the roof deck, formed from a plurality of alternating layers of felt and bituminous material. A thermal insulating layer is then placed over the multiple layers of felt. This thermal insulating layer is generally both water-resistant and, to some degree, water impermeable. A top exterior surface is then applied which consists of a protective layer of mastic and granules.
Another weatherproofing design is disclosed in U.S. Pat. No. 4,016,323. In such a system, a waterproof membrane is applied directly to the surface of a roof deck, and covered with a thermal insulating foam, which is in turn covered by a weather protective elastomer. The waterproof membrane comprises a fiberglass mesh covered by a rubberized material. The membrane has a nontacky bituminous compound on its upper surface. While this design functions adequately for its intended purpose, the fact that the fiberglass portion is not flammable does not mean that the disclosed roof construction is fire-resistant, nor does it suggest that the structure optimally provides a combination of insulating, weatherproof and fireproof characteristics in an adequately lightweight construction.